Hence, for \(c_{s*} \ll 1\)  we have that the spectral tilt, differently
from the previous case, will always be red, since in this case \(n_s-1\propto -(23 + 2 \beta )\) . When \(c_{s*}=1\) , we see from
Eq. (REF ) that \(n_s-1 \propto -(54 - 4 \beta )\)  and the
spectral tilt is, thus, blue for \(\beta > 13.5\) . But in this
case [1]} we have that \(\beta \simeq 4.33\)  (for
\(c_{s*}=1\) ), hence, for large \(Q\)  this dissipation coefficient with a
quartic inflaton potential can quite robustly sustain a red tilted
spectrum. In fact, the effect of having a \(c_{s*} <1\)  here can
potentially make the spectrum too red tilted to be consistent with the
observations, since a value of \(c_{s*}< 1\)  would make the exponent
\(\beta \)  smaller and lead to a redder spectrum. This is confirmed by
our numerical results shown in Sec. . Since this type of
dissipation coefficient already leads to quite satisfactory results
when compared to the observations [2]}, even in
the strong dissipation regime of WI, it is not benefited from a DBIWI
construction, at least in the context of monomial chaotic inflaton
potentials.
